Telecommunication cable is frequently employed in situations where water is able to enter and migrate thoughout the cable system. Water entry into either metallic and fiber-optic cables is undesirable because such entry leads to corrosion and deterioration of desired transmission properties, particularly at the sites where the cables are spliced together.
To protect such cable systems, it has become common practice to encase certain cable segments by a closure that functions as an extension of the cable sheath or cover.
In addition, it has become common practice to encapsulate such cable segments with a curable encapsulant, in order to prevent water migration. Examples of cable segments typically placed in closures and so encapsulated include areas where two or more cables are spliced together, at the ends of cable, junctions between air-pressurized cable and grease-filled cable, and pressure blocks.
It is often necessary for the encapsulant to be re-enterable for repair or other modification. For an enclosure to be re-enterable, the encapsulant must be capable of being entirely removed from around the splice area in a simple manner (such as by hand), because it is not desirable to use tools or other implements near copper wire, optic filament, or delicate parts. In this way, wire and filament connections are not damaged, and copper wire insulation as well as fiber-optic coatings are not disturbed.
Because the splice closures for telecommunication devices are typically encapsulated at field locations where cable is layed, the encapsalants are applied by a variety of individuals under a variety of conditions. It is desirable, therefore, to have a clear, easy to mix, two-part system where adequate mixing can be readily determined from the color change of the system. Sufficient mixing is necessary to obtain high quality splices. Clarity of the encapsalant aids in observation of both the filling process and eventual re-entry process.
Encapsulants of this type are often required to provide acceptable adhesion to grease, because electrical and telephone cables typically contain a number of individual conductors that are often covered with grease as protection from water penetration. U.S. Pat. No. 4,176,240 describes a grease composition which is typical of the types used as water-proofing agents in electrical and telephone cables.
Urethanes which are made by reacting a polyol with an isocyanate, such as those described in U.S. Pat. Nos. 4,375,521; 4,596,743; and 4,666,968, have been described as useful for encapsulation of telecommunication equipment and devices include urethanes.
Urethanes have numerous drawbacks. Urethanes are inherently tough, resilient materials, which renders them inherently difficult to re-enter. Compatability with hydrocarbon-based greases is also poor for urethanes, as is adhesion to grease-coated conductor wires.
In an alternative method of curing polyols, hydroxy-containing compounds are reacted stoichiometrically with maleic anhydride-modified polybutadiene to form thermosetting ester compounds. Organic amines, phosphines and/or organometallic soaps are used to catalyze these esterification reactions. For example, U.S. Pat. Nos. 4,857,563; 4,985,475; and 5,169,716, describe encapsulant compositions which are extended reaction products of an admixture of an anhydride-functionalized composition and a crosslinking agent. Such encapsulants are, however, very difficult to re-enter and adhere poorly to grease-coated wires. The ester linkages formed in these encapsulants are also susceptible to hydrolytic cleavage.
U.S. Pat. No. 5,140,075 describes an encapsulation composition consisting of a low molecular weight epoxy-grafted polymer and a curative. This composition results in a material that is opague, making observation of filling and re-entry more difficult.
It is an object of the present invention to provide a room-temperature curable composition which can be used as a durable encapsulant for signal transmission devices, wherein the encapsulant is easily re-enterable, possesses a high degree of transparency and clarity, is capable of protecting the signal transmission devices from water and other external damage, and has excellent adhesion to grease-coated conductor wires.